Treatment for AIDs associated Pneumocystis carinti pneumonia (PCP), one of the most common opportunistic infections, is routinely based on only two drug therapies; pentamidine and a combination of trimethoprim with sulfamethoxazole. Considerable success has been met in clinical trials using an anti- polyamine agent, DL-alpha-difluoromethylornithine (DFMP, eflornithine), to treat PCP in those AIDS patients refractory or intolerant to the standard treatment protocols - increasingly common phenomena. While the addition of DFMO to the list of drugs for PCP is welcome, the efficacy needs improvement if anti-polyamine therapy is to be a first line treatment for PCP. The rational approach to such improvement is through investigations of parasite polyamine metabolism and of the interaction of the parasite with antipolyamine agents. Despite this, there has been no exploration of polyamine metabolism in Pneumocystis carinii nor any work directed at improving antipolyamine therapy for PCP. DFMO is a highly specific inhibitor of ornithine decarboxylase (ODC), key enzyme for the biosynthesis of polyamines (small molecules having multiple essential functions in all cells). Although it is targeted to a specific enzyme, there is no direct evidence that the effect of DFMO against PCP is by inhibition of the enzyme. Since the enzyme exists in the host and is both essential and sensitive to DFMO, there is no explanation for the selective activity against the parasite. This proposal is focused on confirming the mode of action of DFMO against PCP and determining the basis for its selective action. Improvements of antipolyamine therapy will be sought via basic studies of the polyamine metabolism of the parasite and studies of the effect of administration and the timing of administration of various polyamine biosynthesis inhibitors to the host. the biochemical action of DFMO will be tested by bypassing the putative metabolic block with exogenous putrescine. The basis for the selective action of the drug against the parasite will be addressed by determining the parasite target enzyme drug sensitivity, recovery rate of parasite enzyme activity after inhibition, DFMO penetration of the parasite and drug distribution in the host. Basic biochemical investigation will be made to devise means of improving anti--polyamine activity for treatment of PCP. The rat model of PCP will be utilized for a source of parasites and a model of the disease.